‘HBC 644’ is a product of a controlled breeding program carried out by the inventors in the Yakima Valley of Washington State. ‘HBC 644’ was one of several seedlings resulting from a open pollination cross made in 2008 with female parent ‘CoLT’ (unpatented), and an unknown male parent. The ‘CoLT’ cultivar was created through a chromosomal doubling of the ‘COLUMBUS’ (U.S. Plant Pat. No. 10,956) cultivar, which has a diploid ploidy. The most distinguishing characteristic between the instant cultivar, its maternal parent (‘CoLT’), and a comparison cultivar (‘COLUMBUS’) is the ploidy of each cultivar. The instant cultivar has a triploid ploidy, while its maternal parent ‘CoLT’ has a tetraploid ploidy, and the ‘COLUMBUS’ cultivar has a diploid ploidy.
Seedling plants from this cross were planted in 2009 and screened for disease resistance and sex in a greenhouse and field nursery near Granger, Wash. A single plant of ‘HBC 644’ was selected in 2012 and was asexually reproduced via softwood cuttings in a greenhouse near Toppenish, Wash. In 2013 ‘HBC 644’ was expanded by asexual reproduction via softwood cuttings to 14 plants in an evaluation block near Toppenish, Wash. In 2015 ‘HBC 644’ was further expanded by asexual reproduction via softwood cuttings to a 1 acre test block near Toppenish, Wash. The ‘HBC 644’ plants have now been observed and evaluated for several years. Throughout several generations of asexual propagation, ‘HBC 644’ has been observed to retain its distinctive characteristics and remain true to type.